What is the Tails Doll?
-The Tails Doll is not of this world
-It is neither machine, nor truly alive, and thus it can never die
-It is the antithesis of life
-It is the void in which existence itself is meaningless, and hence suffers eternal hunger. A hunger for the life it can never aspire to.
-It's insatiable appetite is for souls, and yours will do nicely.
-He is every pain you have ever felt, and every illness you have ever feared.
-He is all your darkest secrets, and some that you have yet to discover.
-He is everything and nothing.
-He is the future.
-He is the Omega
-He is slightly orange, and somewhat fuzzy.

*They say it you stare into the abyss for long enough, the abyss stares back. If you stare at the Tails Doll long enough, it will not only stare back, but feast upon your eye balls for the inside as well.

Before death you shall see the Tails Doll, hence making him "death"
At birth you shall see the Tails Doll, hence making him life.
therefor as a simple example, showing how the Tails Doll is "everything, and nothing" or "life, and death" etc.

An evil doll created by Dr. Robotnik that kills people and steals their souls for an unknown purpose. He gets power from a little red light attached to his forehead with a small string. Famous on YouTube. People have tried to impersonate the Tails Doll with crappy animations, fake attack footage, fake sightings, fake photos, etc. His first (and last) appearences were in the game Sonic R. He was a really good character, because he could levitate really fast and float over water, thus allowing him to cheat through the course. He is, of course, fake, so there's nothing to be afraid of.

Jeff: What are you afraid of?
Jenny: The Tails Doll.
Jeff: You're a wuss.